Saleem Abdulrasool 040050a6c7 Basic: out-of-line equality operator (NFCI) ...

MSVC did not like the original code and would fail to build as:

  ```
  swift\include\swift/Basic/Located.h(50): error C2995: 'bool swift::operator ==(const swift::Located<T> &,const swift::Located<T> &)': function template has already been defined
  swift\include\swift/Basic/Located.h(50): note: see declaration of 'swift::operator =='
  llvm\include\llvm/Support/TrailingObjects.h(76): note: see reference to class template instantiation 'swift::Located<swift::Identifier>' being compiled
  llvm\include\llvm/Support/TrailingObjects.h(233): note: see reference to class template instantiation 'llvm::trailing_objects_internal::AlignmentCalcHelper<swift::Located<swift::Identifier>>' being compiled
  swift\include\swift/AST/Decl.h(1512): note: see reference to class template instantiation 'llvm::TrailingObjects<swift::ImportDecl,swift::Located<swift::Identifier>>' being compiled
  ```

The original code is odd.  There appears to be some unnecessary
complexity.

First, the member function is marked as a friend of a
`struct` type which does not change the member's visibility, thus all
the members are `public`, and the function need not be friended.

Second, the function is templated over the same parameter type, which
means that the original template parameter could be used and the
standard member equality operator could be used rather than the
free-standing form.

It is unclear why the member equality operator is insufficient, and the
extraneous template instatiations here seem wasteful.  Out-of-line the
free-standing form and not mark it as a friend to restore the build.
Switching to a member form can be a follow up change.

2020-01-06 15:53:19 -08:00

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